This invention relates to starting of high intensity discharge lamps and, more particularly, to new and improved apparatus for efficiently coupling high voltage, short duration pulses to high intensity discharge lamps.
High intensity discharge lamps, such as high pressure sodium lamps, commonly include noble gases at pressures below 100 torr. Lamps containing noble gases at pressures below 100 torr can be started and operated by utilizing an igniter in conjunction with a lamp ballast. The lamp ballast converts the ac line voltage to the proper amplitude and impedance level for lamp operation. The igniter provides pulses which assist in initiating discharge. The igniter is a relatively large and heavy circuit and is typically built into or located near the lamp ballast.
It has been found that the inclusion in high pressure sodium lamps of xenon as the noble gas at pressures well in excess of 100 torr is beneficial to lamp performance. However, the pulse energy requirements for starting of the discharge lamp increase as the pressure of the xenon included within the lamp increases and the conventional igniter described above does not, by itself, produce reliable starting. Various approaches to starting discharge lamps containing high pressure xenon have been taken. A high voltage pulse is typically coupled to the discharge tube by a conductor known as a starting aid, as shown in U.S. Pat. No. 4,179,640 issued Dec. 18, 1979 to Larson et al. The starting aids shown in the prior art have had the form of a wire wrapped around the discharge tube in a spiral configuration or a wire harness surrounding the discharge tube.
Starting aid configurations which more efficiently couple the starting pulse to the discharge lamp are desirable for several reasons. When starting pulse energy requirements are reduced by efficient coupling, the physical size and cost of the starting pulse generator circuit can be reduced. Physical size of the starting circuit is of particular importance when it is desired to include the starting circuit within the outer jacket of the lamp. Alternatively, more efficient coupling of the starting pulse facilitates starting of discharge lamps having higher starting pulse energy requirements.